Process for making 2-chloro-1,3-butadiene



Julyv 1s, 1940.

A. s. CARTER PROCESS FOR MAKING Z-ACHLORO-l-BUTAIENE Filed Oct. 15, 1937 ATTORNEY Patented July 1s, 1940 UNITED VSTATES l PROCESS FOB VMAKING #CEDRO-1,3-

BUTADIENE Albert s. cai-ter, Wilmington, nel., assigner to E. I. du Pon le Nemours a; Company, Wilmington, Del., a corporation of Delaware Application october 15, 19st, serial'No. 169,168

v4 elimini.A (ci. 26o-s55) g This invention relates to the manufacture of hydrogen halide addition products of vinylacetylene. More particularly it relates to a method for the manufacture of 2-chloro-1.,3butadiene suba stantially free of vinylacetylene.

In the manufacture of 2-chloro1,3.butadiene (hereinafter called chloroprene) by the process described in U. S. Pat. No. 1,950,434, issued March 13, 1934, to Downing, Carter and Hutton,the

` chloroprene leaving the reaction chamber is equipment and also results in theloss of chloro.

prene as polymers. I An object of this invention is the production of hydrogen halide addition products of vinylacetylene substantially free of vinylacetylene. A

further object of the invention is a process of making chloroprene in which the vinylacetylene removed from the chloroprene is returned to the system for further reaction. A still further 0bject is a continuous process of making chloroprene in high yieldsubstantially free of vinylacetylene.

'These Iobjects have been accomplished by strip-y ping the vinylacetylene from the hydrogen halide addition products of vinylacetylene by means of an inert gas andfrecirculating the vinylacetylene v to the reaction system. 4o The single gure of the drawing is a-ow sheet of the process herein described. .When the process of this invention is carried out continuously, beginning with the making of monovinylacetylene from acetylene (for example according to U. S. Pat. No. 2,048,838, issued July 28, 1935, to Carter and Downing) it is advantaeous to use acetylene as the inert gas for stripping monovinylacetylene from chloroprene. VAs is shown in the drawing, acetylene is introduced at so l into a reactor 2 where it is converted in the presence of an aqueous cuprous chloride catalyst 'into nonbenzenoid acetylene polymers. 'I'he emuent gases also contain watervapor andunreacted acetylene'. These gases are passed into a drier# 55 and the water returnedto-the reactcrat 4.

Pressure is then applied at 5 and the temperaz ture is lowered (for example to -'Z0v C.) thereby producing condensation of all of the reaction products. 'I'he unreacted acetylene is not all -condensed and the uncondensed acetylene is vented "5 at 6. The pressure is released at l and the remaining unreacted acetylene is thereupon vaporized and vented at 8. The acetylene returns through conduit 9, valve I0 and conduit' Il to the acetylene supply at I2. The temperature of the 10, acetylene polymers is raised above thel boiling point of monovinylacetylene atA I3 (for example between 18 and 25 C.) and the monovinylacety Iylene passes. oi through conduit i4, storage tank I5,'and thence into reactor I6 at l1. Hydrogen` Il chloride is introduced into reactor I6 at I8, and a mixture of chloroprene (abbreviated CD in the briefing on the drawing) and unreacted monovinylacetylene' is vented at I9 and liqueed in condenser 20. 'I'he mixture then enters about 20 midway up the column 2l where the temperature is raised Ato between 30 and 35 C. Part of the monovinylacetylene is therebyvaporized and vented at 22 and passes back to the reactor through conduit 23. The chloroprene still con- 25 taining an undesirable amount of vinylacetylene leaves-column 2i at 24 and is passed into the packed stripping column 25 at 26, midway up the packed section. Part of the acetylene from conduit 9 'is diverted at valve l0 into conduit 21 90 and it is passed through valve 28 into the strippingvcolumn 25 at 29. As-the acetylene passes up the column, it contacts the chloroprene and l -entrains and removes themonovinylacetylene therefrom. Acetylene and entrained monovinyl- 35 acetylene leave the stripping column `at 30 andI are passed through a reilux condenser 3l to remove any entrained chloroprene. These gases ,then pass through conduit 32, valve 33. conduit 34 and are returned tothe eilluent gases of re- 40 actor 2 at 25. chloroprene substantially free of (containing less than 1%) monovinyla'cetylene Y leaves the stripping'columnat 36.' With the temperature of the column held at 20 to 45 C.,

the liquid is contacted with a sumcient volume 45 of gaseous acetylene to reduce the vinylacetylene content* of the chloroprene to less than 0.5% by analysis. lThe volume of acetylene required isdependent upon the length and diameter of the column and the initial vinylacetylene content of the liquid. `The liquid dischargingfrom the bottom ofthe column contains little or no polymer.

It is to be understood that the acetylene ior the stripping stepneed not be taken from the recovered unreacted acetylene at Il, but may be pendently of the making of 'monovinylacetylena there is no particular advantage in using acetylene in the stripping' column. Any uid which is in the non-liquid state at the temperature and "pressure ,usedl in the stripping operation and which is inert to chloroprene and to monovinylacetylene may be used in the stripping operation. The term inert gas is used to ysignify such a non-liquid fluid. Those inert gases are preferred which satisfy these conditions at a preferred temperature (between 20 and 45 C.) and atmospheric pressure. Examples of such inert gases are nitrogen, carbon dioxide and the inert gases oi the zero group of the periodic table.

Referring again to the ligure and using nitrogen as an example, monovinylacetylene from the storage tank l is introduced into reactor I6 at I'l. Hydrogen chloridevis introduced into the reactor at I8 anda mixture of monovinylacety lene and chloroprene are vented at i9 as before. This mixture is condensed as v and passed linto column 2l where some of the monovinylacetylene is volatilized, vented at 22 and returned to the reactor through conduit 23. The chloroprene with the remaining monovinylacetylene leaves4 column 2l at 24 and is passed into stripping co1- umn 25. 'Valve 28 is closed and nitrogen or other inert, relatively insoluble gas is introduced into stripping column 25 at 31 by opening valve 38.'

The mixture of nitrogen and monovinylacetylene is vented at and passes through reux condenser^3i and conduit 32 to valve 33. Valve 33 is adjusted so that the mixture of gases passes to condenser 39 where the monovinylacetylene is liquefied. Nitrogen is vented from condenser 39 at 40 and is returned to the stripping column at 31. `The monovinylacetylene leaves condenser 39 at 4I, passes through valve 42 andenters the return conduit 23 at 43 for recirculation through reactor I6. Substantially monovinylacetylene free chloroprene leaves the column at 88. When this process is used, it is not essential that the gases effluent from stripping column 25 be free of chloroprene, since the monovinylacetylene may be returned tothe reaction system just prior to thev separation of monovinylactylene and chloroprene. When it is convenient to operate the stripping column with little or no dephlegmation, allowing.l some chloroprene to be stripped out in the gas together with the monovinylacetylene.` the two are condensed together from the stripping gas in condenser 39 and are then introduced directly into the condensate from the condenser 20 at 44 by adjusting valve 42. There is then no need to operate reiiux condenser 3i and itmay, if desired, be used simply as a part of. con-A duit 32 or it may be by-passed. Suitable blowers and pumps not shown in the figure are installed where needed to propel the uids and suitable` valves and tting's are placed where required. It willbe-understood that the iiow sheet is' diagrammatic and that no attempt has .been made to give apparatus details which are unnecessary to an understanding of theinvention. v

Regardless of whether the process is operated with the manufacture of. vinylacetylene, using acetylene in the stripping column, and the eiiluent gases are returned at or whetherthe process is operated independently with monovinylacetyexample, a stripping column packed with copper or glass rings, carborundum, chain or other material suitable for packing-similar column may be used. It may be jacketed with a constant temperature liquid.

The process of this invention may be operated at any convenient pressure. `The use of vacuum assists the process in some respects but the disadvantages generally outweigh the advantages. It is generally most convenient to carry out the gas stripping at or slightly above atmospheric pressure. The temperature of the lstripping operation may be controlled within suitable limits. Since it is an object of this invention to prevent further polymerization by heat, itis desired to keep the temperature as low as possible consistent with efcient stripping. It has been found that the'process can be eiiiciently operated at a temperature of between 20 to 45 C. While` the process is not inoperative at higher temperatures, such temperatures result in a greater tendency of the chloroprene to polymerize. Lower tem-` peratures are also operative butl are less efficient with regard to the amount of gas lrequired for the removal of the volatile impurity.

Specic details for that part of the process which has to do with making monovinylacetylene from acetylene have not been given here since the process is not limited in this regard. Thus, while theprocess of" U. S. Pat. No. 2,048,838 has been referred to for specific disclosure, yet it is within the scope of the present invention to vary that process inany suitable way. For example, the process of vconverting acetylene to monovinylacetylene describedun U. S. application Ser. No.y 151,644, filed July 2, 1937, may be used for this part of the process of the present application. Also monovinylacetylene may be removed from higher acetylene polymers by the process of copending U. S. application Serial No.7169,169 iiled October l5, 1937. Similarly the making of chloro-2butadiene-1,3 from monovinylacetylene may be carried out inany suitable manner. For example, the process of U. S. Pat. No. 1,950,434 may be used 'or the process described in IU, S. application No. 152,518, filed July 8,.1937,'that described in U. S. applicationvNo., 169,192, led October 15, 1937, or that in U. S. application No. 178,929 filed December 9, 1937, may be used.

The essential improvement of the process of the present application resides in the removal of monovinylacetylene from chloroprene" in such manner as to prevent loss of chloroprene as chlo.- roprene polymers or in any other Way. Moreover, this improvement is accentuated in that itis so intimately connected with the'st'eps of making i monovinylacetylene and chloroprene ,that the purification of chloroprene is accomplishedwlth-` ,70'

out the lossof unreacted monov'inylacetirlenaI` which material is returned to the reaction system recirculaung the acetylene through the stripping.

which not infrequently accompany thermal andy l vacuum distillation of chloroprene vto remove monovinylacetylene.

A process has been described for safe and emcient productionl of chloroprene in high yield free of monovinylacetylene. While the process of the invention has been described with reference to the manufacture o! chloroprene, it is obvious that it is likewise applicable to the manufacture of other hydrogen chloride addition products oi vinylacetylene and to the manufacture of hydrogen bromide addition products 'of vinylacetylene by suitable changes in the details of the process. It will be understood that any variations ,or departures from the disclosure which conform to the spirit of the invention are intended to be embraced within the scope of the claims.

I claim:

1.-In a process of'making Z-chJoro-LZi--buta` diene by reacting monovinylacetylene with hydrogen chloride to form 2-chloro-L3-butadiene as a -product of the reaction, the steps of Apartially separating unreacted monovinylacetylene from the crude products, said products in the liquid phase through a stripping zone at a temperature of between 20 C. and V45" C., passing an inert gas through the strippingzone to remove substantially all of the remaining monovinylacetylene from said products, 4and returning the thus removed monovinylacetylene to the reaction system.

zone.

3. In a process of making 2-chloro-L3-butadiene by reacting monovinylacetylene with hydrogen, chloride to form 2-ch1oro-1-butadiene as a productor the reaction, the steps of partially separating vunreacted monovinylacetylene from the crude products, passing said products in the liquid phase through a stripping zone at a temperature of between 20 C. and 45 C.,

`passing nitrogen counter-current through the stripping zone to remove substantially all of the remaining monovinylacetylene, separating the' nitrogen from the monovinylacetylene, returning the monovinylacetylene to the reaction system, and recirculating the nitrogen through the stripping zone.

4. The process or making ii-chloro-La-butadiene which comprises reacting acetylene in a rst reaction zone to produce monovinylacetylene as the principal product, sweeping the gaseous products out of said zone with unreacted acetylene, separating acetylene from the eluent gases of the rst reaction zone, separating monovinylacetylene from the productsof the rst reaction zone, reacting the monovinylacetylene with hydrogen chloride inl a second reaction zone to form 2chloro1,3butadiene as the principal product, sweeping the gaseous products out of the second reaction zone with unreacted monovinylacetylene, partially removing monovinylacetylene. from. the products of the second reaction zone, said products in' the liquid phe 4through a stripping. zone atv 20 to 45 C., and acetylene countercurrent through the stripping zone to' remove substantially all of the remaining monovinylacetylene, 'nefluxing the ellluent gases of the stripping zone to retain 2-chloro-1-butadiene and passing the acetylene and monovinylacetylene emuent from the shipping zone into the effluent gases of the iirst reaction zone at apoint in the process prior to the removal of acetylene i'romtheemuentgasesoftherstzone.

AIBIRT S. CARTER. 

